Magnetic response of an electron gas in a quantum ring of non-zero width

An investigation of the magnetic moment of an electron gas in a quantum ring of non-zero width is made. Analytic expressions are obtained for the magnetic moment. For the magnetic moment of the system, the dependence on temperature and parameters of the ring are found and investigated in detail. De Haas–van Alphen and Aharonov–Bohm oscillations are investigated.     

First-principles calculations of the structural, electronic and magnetic properties of BnN20−n (n = 6−18) clusters

The structures of B _n N_20 ? n    (n = 6?18), the clusters of boron nitride, are investigated by the density functional theory calculations. The structures of the obtained low-lying isomers can be described by the following six prototypes: single ring, double ring, three-ring, graphitic-like sheet, fullerene and others. B₁₀N₁₀ is demonstrated to be the most stable cluster against the nonstoichiometric ones. Nonzero magnetic moments, 1.999, 1.998, 2.000, 3.999 and 1.999μ _B respectively, are found in five B _n N_20?n (n = 6, 7, 11, 12, 13) clusters. Further analysis indicates that the magnetic moment of the B₆N₁₄ cluster is mainly originated from the N atoms, while those of others are from the B atoms. The magnetic moment are finally attributed to the interesting issues of the 2p electrons due to the breaking of local symmetries, the change of coordination number, charge distribution and orbital hybridization.     

Neutrino self-energy operator and neutrino magnetic moment

A simple method for calculating the magnetic moment of a massive neutrino on the basis of its self-energy operator is presented. An expression for the magnetic moment of a massive neutrino in an external electromagnetic field is obtained in the R _ξ gauge for the case of an arbitrary ratio of the lepton and W-boson masses.     

The first principles investigation of ferrite magnetic response with mismatch stress

The quasi-ferrite model is proposed and an appropriate PBE exchange functional with the spin density functional theory(SDFT) is selected for the calculation of the relation between magnetic moment and residual stress in ferrite using a quantum mechanics code. The relationship between ferrite magnetism and the carbon content is determined,and then a ferrite interstitial solid solution(ISS) model in a low carbon concentration state is replaced with an α- Fe model in the case of majority magnetic calculation. The band structure of the loaded-Fe is compared with that of the unloaded α-Fe. The comparison shows that the energy of Fe atomic 3d orbital changes a little,while the energy of electron orbital of iron core below 3d almost keeps unchanged. The relationship between the magnetic moment and the stress appears intermittent due to the Bragg total reflection. The change in the magnetic moment due to lattice mismatch is much larger than that caused by mechanical loading.     

Revelation of Ni magnetic moment in GdNi single crystal by soft X-ray magnetic circular dichroism

Magnetic moment of Ni in GdNi single crystal was studied through the soft X-ray absorption spectra (XAS) and the magnetic circular dichroism (MCD) at the Ni L_2,3-edges and the Gd M_4,5-edges. Our experiment revealed for the first time that the Ni 3d band is not filled completely even at the content of 50 at.% of Gd and the Ni does retain a total magnetic moment coupling antiparallel to that of Gd. This result implied that the Ni in GdNi holds an intrinsic magnetic moment even at 50 at.% of Gd and contradicts the well-known charge transfer model. Further by employing the magneto-optical sum rule, the spin and orbital angular magnetic moment were evaluated and discussed.     

Superstring induced mass and magnetic moment of the neutrino and the time modulation of the solar neutrino flux

The new Yukawa couplings involving heavy matter E₆ fields predicted in the framework of superstring theories are considered as a source of mass and magnetic moment for the neutrino. Given the experimental bound m_ve < 46 eV bounds are derived on the neutrino magnetic moment thus generated. Finally, a scenario is produced where the induced magnetic moment has the correct magnitude (∼10⁻¹¹ μ_B) to explain an alleged depletion or solar neutrino flux during periods of maximum solar activity.     

Ab initio studies of isolated hydrogen vacancies in graphane

We present a density functional study of various hydrogen vacancies located on a single hexagonal ring of graphane (fully hydrogenated graphene) considering the effects of charge states and the position of the Fermi level. We find that uncharged vacancies that lead to a carbon sublattice balance are energetically favorable and are wide band gap systems just like pristine graphane. Vacancies that do create a sublattice imbalance introduce spin polarized states into the band gap, and exhibit a half-metallic behavior with a magnetic moment of 1.00 μ_B per vacancy. The results show the possibility of using vacancies in graphane for novel spin-based applications. When charging such vacancy configurations, the deep donor (+1/0) and deep acceptor (0/−1) transition levels within the band gap are noted. We also note a half-metallic to metallic transition and a significant reduction of the induced magnetic moment due to both negative and positive charge doping.     

Cyclic hydrocarbons: nanoscopic (π)-SQUIDs?

A nonperturbative method for calculating persistent currents in molecules and nanoscopic quantum rings is presented. Starting from the extended Hubbard model on a ring threaded by an Aharonov-Bohm flux, a feedback term through which the current can generate magnetic flux is added. Another extension of the Hamiltonian describes the energy stored in the internally generated field. This model is evaluated using exact diagonalization and an iterative scheme to find the minima of the free energy with respect to the current. The magnetic properties due to electron delocalization of conjugated hydrocarbons like benzene [magnetic anisotropy, magnetic susceptibility exaltation, nucleus-independent chemical shift (NICS)] — that have become important criteria for aromaticity — can be examined using this model. A possible novel mechanism for a permanent orbital magnetic moment in quantum rings analogous to the one in π-SQUIDs is found in the framework of the proposed model. The quantum rings must satisfy two conditions to exhibit this kind of permanent orbital magnetic moment: a negative Drude weight and an inductivity above the critical level.     

The Muon <Emphasis Type="Italic">g</Emphasis> − 2 experiment at Fermilab

Precision measurements of the anomalous magnetic moment of the muon a_μ are a stringent test of the Standard Model. The last measurement of a_μ at Brookhaven National Laboratory (BNL) differs from the Standard Model prediction by 3-4σ: a possible indication of new physics. A successor to that experiment has been constructed at Fermilab, with the aim of reducing the experimental uncertainty by a factor of four to 140 ppb. The measurement technique continues to use the storage ring concept from BNL, with muons circulating in a highly uniform magnetic dipole field. The spin precession frequency is extracted by analysing the modulation of the rate of higher-energy positrons from muon decays, which are detected by 24 calorimeters around the inside of the ring. Compared to the previous experiment, significant improvements have been made in the areas of muon beam preparation, storage ring hardware, field measuring equipment, and detector and electronics systems. In these proceedings, I report on the status of the experiment as of June 2018, presenting an overview of the experiment’s progress, some initial data from the first run, and the anticipated timeline for a new result.     

What is spin-magnetic moment of electron?

We investigate the problem about what the spin-magnetic moment is. The magnetic moment of the Dirac electron in the frame along z-axis is evaluated. This is identified with the spin-magnetic moment of the electron, because there is not any z-component of magnetic moment caused by orbital angular momentum in our frame. The correct value of the spin-magnetic moment and the correct ratio of the spin-magnetic moment to the spin (i.e. g=2) are obtained explicitly. In deriving them, the negative energy solutions of the Dirac equation perform essential roles. We find that the transition current from a positive energy state to a negative energy state causes spin-magnetic moment of the electrons in vacuum. This fact implies that the ratio of the spin-magnetic moment to the spin may change depending on the environments. For example, it may have different values in materials.     

Magnetic moment of the Volcano ring

Explicit analytical expressions for the magnetic moment and persistent current of the Volcano ring are derived. The magnetic moment is investigated as a function of the magnetic field strength and the temperature. The oscillation periods are determined, and the limiting cases of strong and weak magnetic fields are analyzed.     

Noise-induced stability of the oscillatory mode of a system of magnetic dipoles

On the basis of numerical analysis, the dynamics of the magnetic moment of a ring system of ball-shaped bodies is studied under its excitation by a harmonic magnetic field and an additional noise signal. A stochastic effect is discovered, in which the system passes, under the action of noise, to unstable (in the absence of an additional excitation) oscillatory mode of the total magnetic moment with a frequency differing from the harmonic field frequency. The possibility of controlling the noise signal intensity, which is necessary for the realization of this effect, is demonstrated.     

Neutron diffraction study of the magnetic ordering in EuAs3

The magnetic structure of one of the two ordered phases has been determined at 5 K. The magnetic structure is found to be antiferromagnetic with a cell doubling in the c direction of the monoclinic nuclear cell. The centering in the nuclear cell is replaced by anticentering. The collinear magnetic moments are parallel to the b axis. The magnetic moment per Eu atom has been found to be 5.74(6)μ_B which leads to the saturation magnetic moment of 6.5μ_B.     

Effect of the neutrino magnetic moment on the properties of the muon

The effect of the neutrino dipole magnetic moment on the properties of the muon is investigated within the standard model of electroweak interactions and a model based on the SU(2) _L × SU(2) _R × U(1) _B-L gauge group (left-right model). In the case of the Dirac neutrino, muon decay through the channel µ^? → e ^?γ is studied with allowance for the neutrino dipole magnetic moment. It is shown that, both in the standard model supplemented with an SU(2) _L right-handed neutrino singlet and in the standard model featuring two doublets of Higgs fields, radiative muon decay is unobservable. In the left-right model, the contributions of diagrams associated with the neutrino dipole magnetic moment become significant only in the case of a mutual compensation of the contributions of diagrams involving the electromagnetic vertices of charged gauge bosons and singly charged Higgs bosons. At specific values of the parameters of the left-right model, one can then obtain an experimental upper limit on the branching fraction of this reaction. The contributions of the neutrino dipole magnetic moment to the muon anomalous magnetic moment are found for the Dirac and the Majorana neutrino. It is established that, both in the standard model and in the left-right model, values of the neutrino anomalous magnetic moment that are required for explaining the (g ? 2)_µ anomaly are in excess of the theoretical predictions for this moment.     

Distribution of the magnetic scattering amplitudes in the Fe/Cu multilayer investigated by resonant magnetic diffraction with circularly polarized hard X-rays

Resonant X-ray magnetic diffraction profiles were measured for an epitaxial Fe/Cu multilayer using circularly polarized X-rays near the Fe and Cu K-edges. Diffraction intensities were compared with those obtained from the theoretical and empirical models. It is found that the interface Fe moment is reduced to 70% of the inner-layer moment. Concerning the Cu layer, the observed energy dependence of the magnetic diffraction intensities is consistent with that derived from the first-principle band calculation, indicating that magnetic proximity effect in the Cu layer is confined within a few atomic layers near the interface.     

NixPt1−x/Rh(111): A stable surface alloy with enhanced magnetic moments

We have performed ab initio density functional theory calculations to investigate the miscibility and magnetic properties of pseudomorphically grown monolayers of Ni_xPt_1?x surface alloys on a Rh(111) substrate. We find that the formation of this alloy is energetically favored over phase-segregated forms, and its magnetic moment is also enhanced. A significant contribution to this enhanced magnetic moment is found to come from the induced moments on the otherwise non-magnetic elements Pt and Rh. A low concentration of Ni gives rise to a high magnetic moment per Ni atom. We find that a low effective coordination and a high non-spin-polarized density of states at the Fermi level are responsible for these enhanced moments.     

The mass of the muon

It is shown that a classical relativistic charged particle has an anomalous magnetic moment g=4α/3. If such a “dressed” particle with its mass m, charge e, and anomalous magnetic moment g is quantized by a generalized Dirac equation, then the wave equation predicts a second mass m_μ=m_e(3/2α+1). It is suggested that a magnetic portion of the self-energy is quantized.     

Equilibrium configurations and transitions between them in annular magnetic nanodipole systems

The equilibrium states of annular systems of magnetic dipoles have been studied by computer simulation. The bistability conditions under which the total magnetic moment of one of equilibrium configurations is zero, while the magnetic moment of another equilibrium configuration lies in the ring plane and is close to the sum of the magnetic moments of dipoles in the system, have been determined. The realization of other equilibrium configurations has also been demonstrated. We analyze transitions between equilibrium configurations by acting on the system by longitudinal and circular static fields, as well as transitions from the configuration with the maximal magnetic moment of the system to the configuration with zero total magnetic moment after the relaxation of oscillatory regimes excited by a varying field.     

Dynamically generated anomalous magnetic moment in massless QED

In this paper we investigate the non-perturbative generation of an anomalous magnetic moment for massless fermions in the presence of an external magnetic field. In the context of massless QED in a magnetic field, we prove that the phenomenon of magnetic catalysis of chiral symmetry breaking, which has been associated in the literature with dynamical mass generation, is also responsible for the generation of a dynamical anomalous magnetic moment. As a consequence, the degenerate energy of electrons in Landau levels higher than zero exhibits Zeeman splitting. We explicitly report the splitting for the first Landau level and find the non-perturbative Lande g-factor and Bohr magneton. We anticipate that a dynamically generated anomalous magnetic moment will be a universal feature of theories with magnetic catalysis. Our findings can be important for condensed planar systems as graphene, as well as for highly magnetized dense systems as those forming the core of compact stars.     

Neutron diffraction study of RECo2Si2 intermetallics

A neutron diffraction study of polycrystalline RECo₂Si₂ intermetallics (RE = Pr, Nd, Tb, Ho, Er) carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic ordering of +?+? type. Magnetic moment is localized on RE ions only and amounts to the RE³⁺ free ion value. In ErCo₂Si₂ the magnetic moment is normal to the tetragonal unique axis, whereas in the remaining compounds the magnetic moment is aligned along it. Néel points were determined from the temperature dependence of magnetic peak heights.